Difference between >>> and >>

2018-06-28 23:26:04

Java中的操作符>>>和>>什么区别？

>> is arithmetic shift right, >>> is logical shift right.

In an arithmetic shift, the sign bit is extended to preserve the signedness of the number.

For example: -2 represented in 8 bits would be 11111110 (because the most significant bit has negative weight). Shifting it right one bit using arithmetic shift would give you 11111111 , or -1. Logical right shift, however, does not care that the value could possibly represent a signed number; it simply moves everything to the right and fills in from the left with 0s. Shifting our -2 right one bit using logical shift would give 01111111 .

>>> is unsigned-shift; it'll insert 0. >> is signed, and will extend the sign bit.

JLS 15.19 Shift Operators

The shift operators include left shift << , signed right shift >> , and unsigned right shift >>> .

The value of n>>s is n right-shifted s bit positions with sign-extension .

The value of n>>>s is n right-shifted s bit positions with zero-extension .

    System.out.println(Integer.toBinaryString(-1));
    // prints "11111111111111111111111111111111"
    System.out.println(Integer.toBinaryString(-1 >> 16));
    // prints "11111111111111111111111111111111"
    System.out.println(Integer.toBinaryString(-1 >>> 16));
    // prints "1111111111111111"

To make things more clear adding positive counterpart

System.out.println(Integer.toBinaryString(121));
// prints "1111001"
System.out.println(Integer.toBinaryString(121 >> 1));
// prints "111100"
System.out.println(Integer.toBinaryString(121 >>> 1));
// prints "111100"

Since it is positive both signed and unsigned shifts will add 0 to left most bit.

Difference between >>> and >>

JLS 15.19 Shift Operators

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